The invention relates to a device for actuating a cable, comprising a lever which can be pivoted about an axis, a connecting device for connecting the cable pull in an extension-resistant manner to the lever at a distance from the axis which is decreased by pivoting of the lever, and a device for reducing the effective length of the connecting device.
Actuation devices of this type can be used for a wide variety of purposes. In motor vehicles, they are used, for example, for actuating a parking brake. The parking brake is conventionally referred to as a hand brake because it is generally actuated via a hand lever. However, at the same time, foot-actuated parking brakes are also known. The actuation of a brake of this type takes place via a cable, which, however, becomes stretched over the service life of the motor vehicle, or, due to the brake linings becoming worn, the actuating travel changes. If, as a consequence of this stretching, the pivoting of the actuating lever exceeds a permissible angular size, the cable of the brake actuating means has to be reset.
U.S. Pat. No. 5,660,082 shows a device for actuating a cable pull, having a one-armed lever which can be pivoted about an axis, a connecting device for connecting the cable pull in an extension-resistant manner to the lever at a distance from the pivot axis of the lever, in which a U-shaped part having a constant active length is used as the connecting device. The lever has a slotted guide link which is of rectilinear design and in which a coupling element which is connected in an extension-resistant manner to the cable pull is mounted, and the coupling element is guided in the slotted guide link in such a manner that it is displaced, as the lever pivots, in the slotted guide link and decreases its distance from the pivot axis of the lever. A catch which can be adjusted by means of a rotary screw is arranged in the slotted guide link and limits the movement of the coupling element in the slotted guide link when the brake device is actuated. One disadvantage of this type of brakes is that there is no possibility of changing the active length of the cable in order therefore to change the length of the cable pull. This is necessary, for example, if the cable pull has become extended due to the duration of use. In order to compensate for this extension, in the case of the parking brake indicated in said document, a catch is provided for changing the pivoting option of the coupling element, but this has the effect of therefore also changing the pivoting region of the lever and thus, depending on the duration of use of the brake, the actuator has to adjust itself to provide a new performance of the brake. A further disadvantage is that the coupling element of the traction cable is guided in a slotted guide link which results in severe stressing of the coupling element and it is therefore subjected to severe abrasion.
Previously a steel cable which was guided by a roller was used as the traction element. This inevitably led to the traction element being subjected to a bending stress which was repeated on each actuation of the handbrake or the like, reduced the fatigue strength and finally ended with the steel cable breaking and therefore with the failure of the brake.
FR 2 611 832 A3 shows a device for actuating a cable pull with a lever and with a device connecting the cable pull to the lever, the connecting device being designed as a traction rod having a variable active length, so that the effective length of the connecting device can be reduced. A disadvantage of this type of brake device is the fact that the traction rod is connected directly to the lever and therefore, when the brake is actuated, a rubbing effect is produced between the traction rod and the lever, which results in a relatively rapid abrasion of the traction rod.
The previous structural design also had the consequence that a structural space of a certain volume had to be available for the pivoting of the actuating lever connected to the cable pull.
U.S. Pat. No. 5,979,266 shows a device for actuating a cable pull with a lever and a device for connecting the cable pull to the lever. The connecting device comprises a cam driver which is guided in a curved slotted guide link and a cable fastening ring for the attachment of the brake cable. Furthermore, a device for setting the starting position of the lever is provided.